Process for the manufacture of hydrogen peroxide



Lelia s- United States PatentO PROCESS FOR THE MANUFACTURE OF HYDROGENPEROXIDE Charles William Le Feuvre, Luton, England, assignor to La PorteChemicals Limited, Luton, England, a British company No Drawing.Application October 11, 1955 Serial No. 539,935

Claims priority, application Great Britain February 23, 1951 Claims.(Cl. 23-407) This invention relates to an improved process for themanufacture of hydrogen peroxide and is a continuationin-part of myabandoned applications Serial Nos. 270,517, filed February 7, 1952, and435,610, filed June9, 1954.

United Kingdom specification No. 465,070 describes a process for theproduction of hydrogen peroxide by hydrogenating a solution of asubstituted anthraquinone by means of hydrogen in the presence of acatalyst, to form the corresponding anthraquinol or anthraquinhydrone,which is then oxidised by meansof oxygen to reform the anthraquinone,with simultaneous production of hydrogen peroxide, which is thenseparated. The process is thus cyclic. This specification gives asexamples of suitable solvents for the anthraquinols, amyl alcohol,cyclohexanol and methyl-cyclohexanol, while the solvent specified forthe anthraquinone is benzene, toluene, xylene or tetrahydronaphthalene.Various other solvents have subsequently been proposed for use in such aprocess. Thus, in United Kingdom specification No. 508,081 the solventspecified in the example is a mixture of benzene andmethyl-cyclohexanol.

United Kingdom specification No. 669,274 describes the use of a solventmixture consisting of a hydrocarbon constituent for solution of thequinone material and a water-insoluble organic phosphonate fordissolving the anthraquinol. Examples of hydrocarbons given are benzeneand dimethylnaphthalene.

United Kingdom specification No. 671,254 describes a solvent mixturewith the usual hydrocarbon constituent for the quinone form, while thesolvent for the quinol form of the alkylated anthraquinone is atri-substituted organic ester of phosphoric acid. Examples ofhydrocarbons given are benzene and dimethylnaphthalene.

In US. Patent No. 2,215,883 suitable solvent mixtures are, for example,benzene and cyclohexanol, toluene and amyl alcohol, xylene or anisol andisoheptyl alcohol and anisol and methyl-cyclohexanol.

.U.S. Patent No. 2,455,238, however, describes a single solvent havingthe requisite solvent power for the quinone as well as the quinol formand in which both reduction and oxidation can be carried out atrelatively high concentrations of both forms of the workingintermediate. Examples of such single solvents are esters of sebacicacid or the esters of other dibasic organic acids, such as succinic andadipic acid, the molecular structure of the ester containing twelve tosixteen carbon atoms, containing two ester groups and being made from analiphatic or aryl-aliphatic acid and an aliphatic or arylaliphaticalcohol. The specification mentions a number of esters including dip-methyl-cyclohexyl succinate.

United Kingdom specification No. 686,567 describes a solvent mixtureconsisting of the primary and secondary nonyl alcohols and mixturesthereof and a substance selected from the group consisting of themonomethyl The component for dissolving the anthraquinhydrone 2,927,002Patented Mar. 1, 1960 ICE or anthraquinol can also influence the ease ofaqueous extraction of the hydrogen peroxide produced when the othercomponent in the solvent mixture is an aromatic hydrocarbon, e.g.benzene, as the partition coeflicient of hydrogen peroxide between thewater and the solvent mixture depends largely upon it. The solventspreviously proposed, and illustrated above, for dissolving the anthraquinhydrone or anthraquinol had, however, several disadvantages.Thus, cyclohexanol is a good solvent for the anthraquinhydrone oranthraquinol, but it is very soluble in water and is oxidised to adipicacid by hydrogen peroxide. Both amyl alcohol and methylcyclohexanol havean inconveniently high solubility in water. The partition coeflicientsalso of the mixtures of cyclohexanol, methyl cyclohexanol and amylalcohol with the solvent for the anthraquinones are low. Thedetermination of partition coefficients is described in Example 2.

The present invention is based upon the discovery that the acetates andpropionates of cyclohexanol and of alkyl cyclohexanols, particularlymethyl cyclohexanol and preferably methyl cyclohexanol acetates areexcellent solvents for the process either when used alone or ascomponents of solvent mixtures. Preferably the alkyl group or groups inthe alkyl cyclohexanols do not contain more than eight carbon atoms.

The term alkyl cyclohexanol as used herein includes not only theseparate isomers but also a mixture of any or all of the isomers.

Accordingly, the present invention in its broadest aspect provides in acyclic process for the manufacture of hydrogenperoxide by theautoxidation of an anthraquinone derivative selected from the groupconsisting of substituted anthraquinhydrones and substitutedanthraquinols in a solvent to form hydrogen peroxide and a substitutedanthraquinone with the subsequent removal of the hydrogen peroxide byextraction with an aqueous liquid followed by reduction of thesubstituted anthraquinone back to said substituted anthraquinhydrone orsubstituted anthraquinol which is again autoxidised, the step of using asingle solvent or a solvent mixture containing an aliphatic esterselected from the group consisting of acetates and propionates ofcyclohexanol and of alkyl cyclohexanols, but the scope of this inventionincludes both types of solvent.

The use of a single solvent as distinct from a solvent mixture has anumber of advantages as: follows:

(1) It is simpler to use a single solvent than a mixture of solvents. Itobviates the trouble of maintaining the proportion of the two solventsin a solvent mixture.

(2) It obviates the use of benzene and similar solvents with a lowflashpoint, as the cyclohexanol esters have a higher flash point.

(3) Owing to the higher solubility of the quinol form in a singlesolvent, a greater quinol concentration can be used, and hence there isless solution to handle than when using a solvent mixture, for the samehydrogen peroxide output.

Examples of esters suitable for use in the process of the presentinvention are the acetic acid or propionic acid etsers of cyclohexanolor of methyl cyclohexanol (in this latter case the 1, 2, or 3 isomers ora mixture of them).

If a solvent mixture is used the solvent for the quinone may be benzene.Benzene, usually employed as the solvent for the quinone has, however,the serious disadvantage of having a low flash point and high vapourpressure. In addition benzene vapour is highly toxic so that not onlyare there fire risks, but also possible health hazards for the plantoperators. In a process in which gases areblown through a mixturecontaining benzene and then towaste, its low vapour pressurenecessitates an expensive solvent recovery process. It'is thereforeproposed to employ as the solvent for the quinone one or more benzenescontaining one or more alkyl groups, e.g. ethyl or methyl substitutedbenzenes.

In addition to having a higher flash point, the benzenes containingone'or more alkyl groups, eg. ethyl or methyl substituted benzenes, alsohave other advantages. With increasing substitution the vapour pressureand toxicity decrease. Thus, by a suitable choice of solvent, fire andother hazards can be greatly decreased, while the necessity for solventrecovery processes can be largely eliminated. Another advantage is thatthe control of solvent roportions is simplified as this can be difiicultwhen one of the components of the solvent mixture is more volatile thanthe other, which is generally true with 'benzene.

The alkyl substituted benzenes may be, for example, one or more xylenesor one or more trimethyl-benzenes. An example of a suitable methylsubstituted benzene is a proprietary solvent derived from petroleum andhaving a boiling range'of 5% at 155 C. and 95% at 185 C. The proportionof aromatic compounds to parafiinic in this solvent is of the order 4:1.It contains 50% of mesitylene (1:3:5-trimethyl-benzene), 30% ofpseudocumene (1z2z4-trimethyl-benzene) and 1:3:4-trimethylbenzene. Theremaining 20% are paraffinic compounds. The above solvent has a flashpoint of 105 F. and a specific gravity of 0.855; another. similarsolvent has a flash point of 125 F. and a specific gravity of 0.870.Another example is a mixture of xylene isomers, ob-

, tained from a petroleum source, which has a specific gravity of about0.855, with a flash pointof 75 F.

Furthermore, other commercial alkyl substituted benzenesmay housed andif desired may be purified bycon ventional methods before use in theprocess of the present invention;

Theuse of an acetate or propionate of cyclohexanol or of an alkylcyclohexanol results in a number of advantages as compared with thecustomary solvents such as cyclohexanol and amyl alcohol. Thus, theacetates and propionates-of cyclohexanol and alkyl cyclohexanols have alower water solubility and they are more resistant to oxidation;Although the solubility of the anthraquinhydrone or anthraquinol in themis less than in the corresponding cyclohexanol, the hydrogen peroxide ismore easily extracted as they have a higher partition coefficient.

Furthermore, the acetates and propionates of cycloexanol and of alkylcyclohexanols have advantages over the solvents of U.S. Patent No.2,455,238 as is shown by the following experiments comparing thedi-methylcyclohexanol succinate andrnethylcyclohexanol acetate.

A solution of 60 gm. of 2-ethyl anthraquinone in one litreofmethylcyclohexanol acetate was made and its density at 20 C. was foundto be 0.959 gm./cc. A solution of 60 gm. of 2-ethyl anthraquinone in onelitre of di-methylcyclohexanol succinate was made and its density at 20C. was found to be 1.038 gm./cc. These results showed that thedi-methylcyclohexanol succinate would be unsuitable as a single solventbecause the density of the solution would make it inconvenient for waterextraction of the hydrogen peroxide.

The viscosity of the solvent or solvent mixture is of considerableimportance because a high viscosity leads to a slower rate ofhydrogenation, slower filtration, greater difficulty in pumping, etc.The viscosity of methylcyclohexanol acetate is'2.19 centipoises at 20 C.whilst the viscosity of di-methylcyclohexanol succinate is 70.1centipoises at 20 C.

Comparative experiments were carried out in which, forthe solventmixture, a solution was taken containing 90 gin/titre of 2-ethylanthraquinone, in a 50:50 xyleneester solution and hydrogenated using 1gm. of 2% palladium on alumina catalyst in 100 cc. of the solution. Thehydrogen uptake in the. case in which the ester wasmethylcyclohexanolacetate .was 27 cc.,.ofv hydrogen. per.

minute, whilst in the case in which the ester was dimethylcyclohexanolsuccinate it was 11 cc. of hydrogen per minute.

The solubility of the reduced form of the quinone in solvent mixtures,each containing one of the two esters, is also of importance.Determinations of these were made in the following way: The solubilityof the Z-ethyl anthraquinhydrone was determined by hydrogenating asolution of the quinone in the solvent mixture with a suitablehydrogenation catalyst until precipitation of the quinhydrone occurred.The solution was then filtered and shaken with oxygen until thedissolved quinhydrone was oxidised. The concentration of hydrogenperoxide in the oxidised solution was then determined: this wasequivalent to the quinhydrone concentration, or to the quinhydronesolubility. The results were obtained using a 50:50 xylene-ester solventmixture at 20 C. and the results for the quinhydrone solubilityexpressed as equivalent gmjlitre of hydrogen-peroxide areas follows:

Grnt/lit're For methylcyclohexanol' acetate 2.8 Fordi-methylcyclohexanol suc'cinate e 1.9

Thus, clearly the solubility of the quinhydrone is less in the mixturecontaining the succinate than in the mixture containing the acetate.

A further and most important factor favouring the methylcyclohexanolacetate is that it is available at a reasonable price commercially,Whereas the di-methylcyclohexanol succinate is not availablecommercially, and if it were it would be likely to be of higher pricethan the acetate.

The following examples illustrate the invention and the advantagesthereof:

EXAMPLE 1 A 10% w./v. solution of 2-ethyl anthraquinone in a mixture ofequal volumes of benzene and 96% methyl cyclohexanol acetate was made.This solution was hydrogenated with hydrogen in the presence of a nickelcatalyst at 20 C. for two hours so that 46% of the 2-ethyl anthraquinonewas reduced to the 2-ethyl anthroquinhydrone. After separation from thecatalyst, the quinhydrone solution was autoxidised by blowing airthrough it, reforming the quinone with simultaneous formation ofhydrogen peroxide. The hydrogenperoxide was extracted from the solutionby passing it through a conventional plate column counter-current to astream of water. The recovery of hydrogen peroxide was 99% and theconcentration in the extract was 162 gm. per litre of hydrogen peroxide.I

It will be seen that the use of such a solvent mixture can give a highconcentration of hydrogen peroxide in the aqueous extract with ahighpercentage of recovery of hydrogen peroxide.

The suitability of a solvent for use in the processof the presentinvention may be measured by determining the concentration ofanthroquinhydrone or its derivative in a saturated solution, and themaximum concentration of hydrogen peroxide in aqueous solution which maybe extracted with water from the organic solution after theanthraquinhydrone has been autoxidised to the anthraquinone withsimultaneous formation of hydrogen peroxide. Determinations of thesewere made in the following way: The solubility of the 2-ethylanthraquinhydrone was determined by hydrogenating a solution o'f'thequinone in the solvent mixture with a suitable hydrogenation catalystuntil precipitation of the quinhydrone occurred. The solution .was thenfiltered and shaken with oxygen until the dissolved quinhydrone wasoxidised. The concentration of hydrogen peroxide in the oxidisedsolution was then determined; this was equivalent to the quinhydroneconcentration, .orto thequinhydrone solubility.

The following results have been obtained under the conditions. of the.example. given above, using. 2 ethyl anthraquinhydrone as {theautoxidisable agent, dissolved in a mixture of. equal volumes of theester and of benzene at 20 C. the former acting as a solvent for the2-ethyl anthraquinhydrone, and containing some ofthe Z-ethylanthraquinone.

Composition of solutions initially containing 100 gm./ litre of Z-ethylanthraquinone, which were reduced until they were just saturated withthe quinhydrone 1 Ester Concentra- Concentra- Maximum content tlon oftion of H201 coni of ester 2-ethyl 2-ethyl centration' Estercompoanthraanthraquin extracted nent, qulnone hydrone (grams percent perlitre, per litre, per litre) grams grams cyclohexanol acetate. 98 41.558.5 180 Oyclohexanol proplonate 99 58. 42. 0 290 96% methylcyclohexanol acetate 97 54. 0 46.0 345 l Theproperties of the solventmixture may be varied within limits by altering the proportions of esterand benzene, thus altering the maximum concentrations of theanthraquinone and the anthraquinhydrone which can be used, and also themaximum extractable hydrogen peroxide concentrations. This isillustrated by the following results:

As above, but initially containing 100 gm./ litre of Z-ethylanthraquinone or, where the solubility was below this value, saturatedwtih Z-ethyl anthraquinone Percent Concentra- Coneentra- Maximum ofester tion of tion of H 01 conin 2-ethyl 2-ethy1 centration Estermixture anthraanthraquinextracted by quinone hydrone (grams per volumeper litre, per litre, litre) grams grams 99% cyclohexanol propionate 6517 53 265 7Do.. l l l.- 50 58 42 290 96 0 met y cyc hexanol acetate. 7068 240 D0 60 23 57 235 D0 50 54 46 345 As above, but initiallycontaining 100 gm./ litre of Z-ethyl anthraquinone Concentra- Concentra-Maximum tion of tion of H102 con- Ester content of ester 2 ethyl 2-ethylcentration component, percent anthraanthraquinextracted 1 quinonehydrone (grams per per 'itre. per litre, litre) grams grams 4s. 5 s1. 5l 370 45. 5 54. 5 300 38.5 61. 5 270 EXAMPLE 2 The solubility of 2-ethylanthraquinone in a mixture of equal volumes of methylcyclohexanolacetate (97.5% ester content) and I. Benzene with a flashpoint of 12 F. II. A methyl substituted benzene with a boiling range of5% at 155 Grand at 185 C. and a flash point of F.

III. A methyl substituted benzene as above but with a flash point of F.

at 25 C. is greater than 80 gms./litre in each of the solvent mixtures.This shows that the solubility of the anthraquinone is not excessivelyreduced by replacing benzene by these substituted benzenes.

Solutions of Z-ethyl anthraquinone were made in the solvent mixturesdescribed above. The dissolved 2-ethyl anthraquinone was thenhydrogenated with hydrogen in the presence of a palladium catalystsupported on ac tivated alumina. The hydrogenation process was continueduntil 2-ethyl anthraquinone was completely converted to 2-ethylanthraquinol. After standing for 24 hours at 25 C. the. catalyst and theprecipitated anthraquinol were filtered from all three solutions and theconcentraion of anthraquinol remaining in solution in each mixture wasdetermined. The results were as follows:

Solubility of 2-ethyl Solubility anthraquinol Solvent mixture of 2-ethylas the equianthraquinol valent (gms./litre) hydrogen peroxide(gmsJlitre) I 15. 4 2. 20 II--- 15. 8 2. 26 15. 5 2. 2 1

determmed. The results were as follows:

Concentration Concentration of 2-ethyl of 2-ethyl anthraquim Solventanthraquinhydrone as hydrone equivalent (guns/litre) hydrogen peroxide(gms/litre) I -45. 5 3. 3 II 45. 5 3. 3

The above results show that the replacement of the benzene by .asubstituted benzene does not aifect the solubility of the Z-ethylanthraquinhydrone.

Portions of the solvent mixtures I, II and III described above wereshaken with an equal volume of 15% aqueous hydrogen peroxide at 25 C.until equilibrium was reached. The two phases were then separated andthe hydrogen peroxide concentration in each determined. The partitioncoeiiicient of hydrogen peroxide between the two phases was thencalculated by dividing the concentration in the aqueous phase by theconcentration in the organic phase. Thus the results were as follows:

The above results show" thatthe partition coefiicient and hencethemaximum hydrogen peroxideconcentration which is obtained bymultiplying the' partition coefficient by the quinhydrone solubility asthe equivalent hydrogen peroxide, which may be extracted fromsolutionsinthe mixtures, is not adversely affected by replacing thebenzene by the substituted benzene.

A solution of 70 gms./ litre of Z-ethyl anthraquinone in solvent mixtureII described above was passed through a hydrogenator, oxidiser and acounter-current water-filled plate column. The solution was passedthrough at such a rate that one complete cycle took about three hours.It was then returned to the hydrogenator. A catalyst, consisting ofpalladium supported on activated alumina, was used in the hydrogenatorand this catalyst was continuously separated from the hydrogenatedsolution before the solution passed to the oxidiser. The concentrationof hydrogen peroxide in the oxidised organic solution was 2.5 gms./litreand in the aqueous extract 70 gms. litre. The efficiency of extractionwas greater than 95%.

EXAMPLE 3 The solubilities of 2-ethyl anthraquinone and of Z-ethylanthraquinol were determined in a mixture of equal volumes of methylcyclohexanol acetate (98% ester content) and of a commercialsulphur-free xylene, using the method described above.

The solubility of the quinone was found to be 104 gms/litre and of thequinol was 14.7 gms./litre,- equivalent to 2.1 gms./litre of hydrogenperoxide.

The partition coefficient of hydrogen peroxide between water and thesolvent mixture was also determined in the manner described above, andfound to be 104.

These results show that benzene can be replaced by xylene in the solventmixture without any unfavourable effects on its properties as a solvent.In addition, the flash points of the solvent mixture containing benzeneand 100 gms./ litre of 2-ethyl anthraquinone, and that containing xyleneand 100 gms./litre of Z-ethyl anthraquinone, were determined and foundto be less than 32 F. for the former and 96 F. for the latter. This isan indication of the reduction in the fire hazard following thesubstitution of benzene.

A solution containing 80 gms. of 2-et-hyl' anthraquinone in each litreof a mixture of equal volumes of the commercial sulphur-free xylenereferred to above and of methyl cyclohexanol acetate, was passed througha hydrogenator, oxidiser and counter-current water-filled plate column,where the hydrogen peroxide formed was extracted; the extracted oganicsolution was then recycled. A catalyst consisting of palladium onactivated alumina was used in the hydrogenator, and was continuouslyseparated from the hydrogenated solution before the solution wasautoxidised. The mean concentration of Z-ethyl anthraquinhydrone in thehydrogenated solution was 41 gms./litre, equivalent to a hydrogenperoxide concentration of 2.9 gms./ litre. The mean concentration ofhydrogen peroxide in the aqueous extract was 147 gins/litre and theefficiency of extraction Was 96%.

EXAMPLE 4 The solvent mixture II referred to above, containing 70gms./litre of Z-ethyl anthraquinone, was used in a cycle as outlined inExample 2. In this case, the hydrogenation catalyst was palladiumsupported on magnesium hydroxide. The mean concentration of Z-ethylanthraquinhydrone in the hydrogenated solution was 42.5 gms./ litre,equivalent to 3.05 gms/litre of hydrogen peroxide.

The mean concentration of hydrogen peroxide in the aqueous extract was156 gms./litre, and the efiiciency of' extraction was over 99%.

EXAMPLE 5 may be measured in partby determining, firstly, the

to be cycled through the plant to give a certain yield of hydrogenperoxide, and the maximum concentration of aqueous hydrogen peroxidewhich may be obtained from the cycle directly.

7 Thus, for example, in the case of methyl cyclohexanol acetate used inconjunction with 2-ethyl anthraquinone the use of methyl cyclohexanolacetate alone differs from the use of mixtures of the said ester with ahydrocarbon as a solvent because, in the single solvent, the quinonesolubility is much closer to the equivalent quinol solubility than wasthe case with the solvent mixture. This means that reduction of asaturated solution of the quinone may be taken beyond the halfway stage(quinhydrone) without precipitation of the reduced compounds, so thatthe saturated reduced solution contains both quinhydrone and excessquinol; or the anthraquinone may be completely converted to the quinol.In the following table, the solubilities of the reduced form are shownas the equivalent hydrogen peroxide concentration in the solution, thespecies in solution being the quinol. Comparative results obtained forthe solutions at 20 C. are as follows:

96% Methyl 96% Methyl cyelohexanol cyclohexanol acetate. acetate]benzene (1:1).

Maximum concentration of H202 which may be extracted (EH20:concentrationXpartition co-eiiicient) 219 209 Notes on the above table:

(1) The values quoted are for gms. per litre of solution.

(2) Determinations of quinhydrone and quinol solubilities were carriedout as described in Example 2ab0ve. p 7

(3) Determined as described in Example 2 above using 15% aqueoushydrogen peroxide.

EXAMPLE 6 A solution was made up, containing 46.8 grams of 2-ethylanthraquinone per litre of methyl cyclohexanol acetate. This solutionwas hydrogenated with hydrogen in the presence of a catalyst consistingof palladium supported on activated alumina, so that the catalyst was infree suspension in the hydrogenator. Hydrogenated solution was withdrawnthrough a filter and autoxidised by air blowing. When the anthraquinolformed during the hydrogenation stage was oxidised, it re-formed theanthraquinone with the simultaneous formation of hydrogen peroxide. Theoxidised solution was then passed through a conventional plateextraction column, countcr-current to a stream of water, so that thehydrogen peroxide was extracted into the aqueous phase. The extractedorganic solution was then returned to the hydrogenator and recycled.

The total volume of solution in the system was litres, the volume ofsolution in the hydrogenator was 10 litres, and the rate of circulationof the organic solution was 0.3 litres per minute During thehydrogenation stage, 67.5% of the quinone was converted to quinol, andthe mean concentration as grams per litre of equivalent hydrogenperoxide was 4.41. During the oxidation stage, the average conversion ofquinol to hydrogen peroxide was 97%, and the hydrogen peroxidewasextracted as an aqueous solution containing' l0i95% of hydrogenperoxide, with an" overall extractioaefficiency of 91%.

I claim:

1. In a cyclic process for the manufacture of hydrogen peroxide by theautoxidation of an anthraquinone derivative selected from the groupconsisting of substituted anthraquinhydrones and substitutedanthraquinols in a solvent to form hydrogen peroxide and a substitutedanthraquinone with the subsequent removal of the hydrogen peroxide byextraction with an aqueous liquid followed by reduction of thesubstituted anthraquinone back to said substituted anthraquinhydrone orsubstituted anthraquinol which is again autoxidised, the step of using asolvent containing as a first component for dissolving saidanthraquinhydrones and anthraquinols an aliphatic ester selected fromthe group consisting of acetates and propionates of cyclohexanol and ofmethyl cyclohexanol and a second component for dissolving saidanthraquinones.

2. A process as claimed in claim 1 wherein said aliphatic ester ismethyl cyclohexanol acetate.

3. A process as claimed in claim 1 wherein said aliphatic ester iscyclohexanol acetate.

4. A process as claimed in claim 1 wherein said aliphatic ester iscyclohexanol propionate.

5. A process as claimed in claim 1 wherein said second component fordissolving said anthraquinone is selected from the group consisting ofbenzene and alkyl substituted benzenes.

6. A process as claimed in claim 5 wherein said second component isbenzene.

7. A process as claimed in claim 5 wherein said second component istrimethyl benzene.

8. A process as claimed in claim 5 wherein said second component isxylene.

9. In a cyclic process for the manufacture of hydrogen peroxide by theautoxidation of an anthraquinone derivative selected from the groupconsisting of substituted anthraquinhydrones and substitutedanthraquinols in a solvent mixture to form hydrogen peroxide and asubstituted anthraquinone with the subsequent removal of the hydrogenperoxide by extraction with an aqueous liquid followed by reduction ofthe substituted anthrauinone back to said substituted anthraquinhydroneor substituted anthraquinol which is again autoxidised, the step ofusing in said solvent mixture as a component for dissolvingsaidsubstituted anthtraquinhydrones and said substituted anthraquinolsan aliphatic ester selected from the group consisting of acetates andpropionates of cyclohexanol and of methyl cyclohexanol.

10. A process as claimed in claim 9 wherein said aliphatic ester ismethyl cyclohexanol acetate.

References Cited in the file of this patent UNITED STATES PATENTS2,158,525 Riedl et a1. May 16, 1939 2,215,883 Riedl et al Sept. 24, 19402,455,238 Dawsey Nov. 30, 1948 2,660,580 Von Nov. 24, 1953 FOREIGNPATENTS 519,509 Belgium May 15, 1953

1. IN A CYCLIC PROCESS FOR THE MANAFACTURE OF HYDROGEN PERIOXIDE BY THEAUTOXIDATION OF AN ANTHRAQUINONE DERIVATIVE SELECTED FROM THE GROUPCONSISTING OF SUBSTITUTED ANTHRAQUINHYDRONES AND SUBSTITUTEDANTHRAQUINOIS IN A SOLVENT TO FORM HYDROGEN PERIOXIDE AND A SUBSTITUTEDANTHRAQUINONE WITH THE SUBSEQUENT REMOVAL OF THE HYDROGEN PERIOXIDE BYEXTRACTION WITH AN AQUEOUS LIQUID FOLLOWED BY REDUCTION OF THESUBSTITUTED ANTHRAQUINONE BACK TO SAID SUBSTITUTED ANTHRAQUINHYDRONE ORSUBSTITUTED ANTHRAQUINOL WHICH IS AGAIN AUTOXIDISED, THE STEP OF USING ASOLVENT CONTAINING AS A FIRST COMPONENT FOR DISSOLVING SAIDANTHRAQUINHYDRONES AND ANTHRAQUINOLS AN ALIPHATIC ESTER SELECTED FROMTHE GROUP CONSISTING OF ACETATES AND PROPIONATES OF CYCLOHEXANOL AND OFMETHYL CYCLOHEXANOL AND A SECOND COMPONENT FOR DISSOLVING SAIDANTHRAQUINONES.